Membrane contactors including hollow fiber membranes are used in many industries to modify the concentration of a predetermined substance in a fluid (i.e., a liquid or a gas). The hollow fiber membranes are porous hollow fibers, which selectively allow for the transfer of molecules through the wall of the hollow fiber membrane. The transfer of the molecules through the wall of the hollow fiber membrane is facilitated by a chemical concentration gradient between a fluid inside of the hollow fiber membrane and a fluid outside of the hollow fiber membrane. Because the membrane contactor facilitates the transfer of molecules through the wall of the hollow fiber membrane, the membrane contactor is said to bring about “contact” between the fluid inside of the hollow fiber membrane and the fluid outside of the hollow fiber membrane.
Since hollow fiber membranes allow only molecules of a predetermined substance to pass through the hollow fiber membrane, they can be used to separate molecules from various materials. In fact, different hollow fiber membranes are used for different applications because the characteristics of the hollow fiber membrane affect the number and type of molecules that can be selected.
One example of the use of membrane contactors including hollow fiber membranes is in the process of removing dissolved gases (e.g., O2 and N2) from water. During the gas-removal process, water containing dissolved gas flows past the outside (“shellside”) of the hollow fiber membranes. A vacuum or sweep gas (e.g., N2) is maintained in the inside (“lumen”) of the hollow fiber membranes. The concentration gradient between the water outside of the hollow fiber membranes and the vacuum or gas inside of the hollow fiber membranes results in the transfer of dissolved gases, from the liquid phase to the gas phase, through the walls of the hollow fiber membranes.
Hollow fiber membranes are advantageous in that they allow for the transfer of molecules between fluids inside and outside of the hollow fiber membranes while maintaining physical separation of the two respective phases. Also, hollow fiber membranes offer a large surface area over which the transfer of molecules can occur. However, existing membrane contactors provide relatively low flow capacity, typically between 1 and 200 gallons per minute, and thus, do not offer the economy of scale needed for large-scale applications. Also, existing membrane contactors are expensive to fabricate, have a low tolerance for turbid water, and are difficult to clean and maintain. Accordingly, there is a need for a membrane contactor that facilitates high-flow capacity, provides for economy of scale, and is easy to clean and maintain. The present invention satisfies this need.